Arrangement for electro-magnetically sustaining the movement of a spiral balance spring



R. FAVRE 3,028,532

2 Sheets-Sheet 2 April 3, 1962 ARRANGEMENT FOR ELECT RO-MAGNETICALLY SUSTAINI THE MOVEMENT OF A SPIRAL BALANCE SPRING Filed June 21, 1957 IIIIIII" QMvznPor: R 4 FAVRE r A-Hormty United f Statfis atent".

ARRANGEMENT FOEELECTRO-MAGNETICALLY SUSTAINING THE MOVEMENT OF A SPIRAL BALANCE SPRING Robert Favre, Lausanne, Switzerland, assignor to Fabriques Movado, La Chaux-de-Fonds, Switzerland, a Swiss firm Filed June 21, 1957, Ser. No. 667,216

Claims priority, application Switzerland June 22, 19:6

11 Claims. (Cl. 318132) The present invention has for its object an arrangement for electro-magnetically sustaining the movement of a'spiral balance spring.

This arrangement is of the type constituted'by a magnetic circuit including a section rigid with the balance wheel and a stationary section and byan electric circuit designed so as to transmit in its turn through the agency of the magnetic circuit the impulses which are adapted to sustain the movement of the balance wheel.

Now according to the present invention, there is provided a magnetic screen protecting the oscillating section of the magnetic circuit with a view to removing the disturbances arising during operation under the action of parasitic magnetic fields and to uniformizing the mag netic potential of the medium inside which said section oscillates seas to ensure the astatic equilibrium of the balance wheel.

The accompanying drawings illustrate by way of example five embodiments of the arrangement according to the invention together with various electric circuits adapted to be associated with said embodiments. In said drawings:

FIG. 1 is a plan view of a first embodiment.

FIGS. 2, 3 and 4 are similar views of three further embodiments.

FIG. 5 is a cross-sectional view through line V--V of FIG. 4.

FIG. 6 is a partial view of a detail modification.

FIGS. 7 to 11 are wiring diagrams adapted for use with the arrangements according to FIGS. 1 to 6.

The embodiment illustrated in FIG. 1 includes a magnetic circuit constituted by a stationary section formed by a soft iron armature 10 and a section rigid with the balance wheel and formed by a magnetized bar 11 rocking inside the space defined by two arcuate extensions 12 formed at the ends of the armature coaxially with the balance wheel. Said armature in the shape of a U carries over its medial section a coil 13 formed by two elementary windings 14 and 15 connected with a transistor T and with a battery P, the connections being provided in the manner illustrated in any of FIGS. 7 to 11.

The angles a and 7 through which the observer standing along the axis of the balance wheel sees the gaps between the arcuate extensions 12, Le. across the poles of the magnet formed by ll are equal to only a few degrees, and at the utmost to about The operation of this arrangement is as follows:

At the moment at which the magnetized bar 11 passes through its medial position illustrated in FIG. 1, the magnetic flux passing through the coil 13 is suddenly reversed, this reversal produces in the winding 14 an electric'impulse which starts a current in the circuit of the transistor T which is normally locked and this produces thus a secondary impulse in the winding 15. The latter impulse produces in its turn a modification in the magnetic field passing through the armature 10 whereby the magnetll is subjected to an impulse adapted to sustain the movement of the balance wheel.

It will also be remarked that the arcuate extensions .1! do not only lead to a reversal of the flux in the armare but that they also form a magnetic screen for the 3,028,532 Patented Apr. 3, 1962 magnet 11; said screen cuts out, on the one hand, the disturbances produced in operation as a consequence of the parasitic magnetic fields which may arise and, on the other hand, it uniformizes, except for a well defined area corresponding to the are 5, the magnetic potential of the medium in which the magnet oscillates.

The embodiment illustrated in FIG. 2 is a modification of that illustrated in FIG. 1. According to this modification, the magnet 11 is provided with four poles while the soft iron armature includes two symmetrical sections 10 and 10 terminating each with two arcuate extensions 12 and 12 or 12 and 12.; extending each over 'an angle equal substantially to one quarter of a circumference. The two windings 14 and 15 surround respectively theouter central parts of the two armature sections.

This last arrangement shows the advantage of cutting out a large fraction of the mutual inductance between the windings and this advantage may in certain'case be quite important.

This mutual inductance is entirely eliminated in the case of the embodiment illustrated in FIG. 3 which forms a second modification of the embodiment illustrated in FIG. 1. As a matter of fact, the windings 14 and 15 are each subdivided in the case of FIG. 3 into two halfwindings these half-windings being fitted respectively over the outer parts of the four sections 10 10 forming together the rigid armature 10 and interconnected two by two by the arcuate extensions 121 l 124.

The advantages of the arrangements described hitherto are numerous and in particular there should be mentioned:

The rapid reversal of the magnetic fluxallows obtaining an impulse the amplitude of which is suflicient for sustaining the movement of the balance wheel by means of a small number of convolutions and of a magnetic field of a reduced intensity.

The balance wheel is astatically equilibrated by reason of the constancy of the magnetic potential throughout the range of elongation.

The magnetic losses are very small by reason of the small value of the magnetizing field and of the absence of any parasitic or stray magnetic field.

The balance spring has a very stable characteristic guge since it is subjected to a very reduced magnetic The terrestrial magnetic field exerts no influence on the arrangement by reason of the screening provided by the arcuate extensions.

The passage of the balance wheel through its medial position generates a single impulse instead of a couple of impulses of opposite directions as in the case for all other prior methods and thereby the efiiciency of the arrangement is. increased.

'In contradistinction with all prior methods and means, the remanent magnetism of the armature does not lead to any braking of the balance wheel after the sustaining impulse is produced.

Experimentation has shown that the most favorable angles [3 and 'y are comprised respectively between 1 and 5 and between 3 and 20.

: The arrangement illustrated in FIGS. 4 and 5 includes an armature 20 made of magnetic material showing no 'remanence such as that sold under the name of Ferroxnected as in the case 'of'the 3 winding 13 of FIGS. 1, 2 and 3 with a transistor Tand a battery P in any of the man-v ners disclosed in FIGS. 7 to 11 for instance.

, The magnetic bar 21 is enclosed inside a stationary magnetic screen 23. The latter includesa casing having a cylindrical 'wall Ztboaxially surrounding the balance wheel and the diameter of which is slightly larger than that of the magnet, said'cylindrical wall being associated with two circular plates 25 arranged at short distances from the upper and lower surfaces of the magnet respectively.

'Said casing is provided with'lateral openings 26 located in registry with'the ends of the armature and the breadth of which is substantially equal to that of said ends of the latter and also to that of the magnet 21. Said casing is made of non-remanent magnetic material similarly to the armature 12, but its reluctance with reference to the magnetic flux of the magnet21 is less than that of the armature "29.

This screening provides for the'uniformity of the magnetic potential of the medium inside which the bar oscillates except for the comparatively narrow angular per- 'fectly defined area which registers with the openings 26.

When the poles of the magnetic bar are shifted away from the ends of the arrnature20, the lines of force passing through magnet 2 1 c'lose solely through the stationary screen 23. In contradistinction, when the poles of the magnetic bar occupy a position adjacent the openings '26, a fraction of the magnetic flux passes through the armature 20. Since the reluctance of the latter is higherthan that of the screening casing, the magnet 21 is subjected in this latter position to a force which urges. it away from the medial position illustrated in dot-and-dash lines in FIG. 4. v

These conditions are favorable because this repelling action appearing during the oscillation of the balance wheel as soon as the bar 2\1.is near the openings 26 is speedily replaced by an attractive force produced by the passage of ,a current impulse through the coil 22 as a consequence of the release of the electric circuit due to the passage of a fraction of the magnetic flux fromi the magnet 21 into the armature 20.

This attractive force should in principle disappear as soon as the bar passes through its medial position. At this moment, it is again subjected to a repelling force which continues the driving action of the attractive force. If the attractive force is not wiped out when the magnet passes through its medial position, said magnet is braked; .thisbraking may be used for obtaining an automatic adjustment of the amplitude of the movement of the balance .Wheel since it appears as soon as the speed of the latter passes beyond a predetermined value.

The arrangement illustrated in FIGS. 4 and 5 may be modified to form a fifth embodiment when the armature 20 of magnetic material showing no remanence is replaced i by a :slightly magnetized armature and the magnetized bar 21 is replaced by a bar of magnetic material showing no remanence.

In this latter case, the ,flux generated by the armature 20 is closed over the screening casing whenever the bar 21 is shifted away from its medial position while it passes through the bar when the latter is near registry with the openings 26.

Consequently, when the balance wheel oscillates, the .reluctance of the magnetic circuit decreases as soon as .the bar 11 reaches a position near the poles of the armajcure. This modifies the magnetic conditions in said armature. The release of the electric circuit thus obtained produces a current impulse in the winding 22 which impulsemakes an attractive force act on the bar 21.

As in the reverse arrangement, said attractive force should disappear at the moment of the passage of the :bar through its medial position, failing which the latter istbraked. This leads to the same possibility of adjustingthe amplitude of the balance wheel as in the precedingly described embodiment. I

FIG. 6 illustrates a modification of the magnet shown in FIGS. 1 and 4. Said modified magnet is in the shape of a bar of which the central section is broader than its terminal sections and it carries .alongthe surfaces limiting laterally said central section two blades 27. The latter extending at small distances from the lateral surfaces of the terminal sections of a reduced breadth -.of the magnet collect all the lines of force passing through the latter, ex- 7 cept those which pass through its polar surfaces and which serve for modifying the magnetic condition of the armature.

Said blades have for their chief advantage the fact that they ensure a clean and rapid modification of the magnetic'condition of the armature 10 or 20 as the case. may

' netic circuit may be replaced by the magnetizationpro- 'duced by 'a coil and the duration of which is limited to that of the impulse, wliicharran'gement improves jthe eificiency. i I

What 'I claim is: a

1. An arrangement for electro mechanically maintainingthe movement of a spiral balance wheel, comprising at least one bar of magnetic material diametrically rigid with the balance wheel and oscillating therewith, and including lateral longitudinally extending projections rigid with the oscillating bars and adapted to collect all the lines of force passing out of the said bars, exceptthose which pass through the polar surfaces of the bars, a magnetic circuit including a stationary section, the stationary section, being-made of a magnetic material-showing no remanence, and the oscillating bars being'made of a permanent magnet material, a stationary cylindrical magnetically screening casing, made 'ofa magnetic material showing'no substantial remanence, surrounding the path followed by the ends of the bars at a small distance beyond same and provided with a number of diametria the stationary section, the ends of which face outwardly 'the casing gaps, said casing separating the bars from the stationary section and its gaps registering with the ends of the bars each time the balance wheel is in its medial position of unstable equilibrium, the lines of force produced by the permanent magnets constituted by thebars and which pass through its polar surfaces closing solely through the casing when the balance wheel is awayfrom its medial position and both through the casing and the stationary section when the balancewheel is approximately in said medial position, and an electric circuit wound over the stationary section of the magnetic circuit and subjected to the magnetic pulses produced by the movement of the bars in front of the gaps to produce in its turn modifications in the flux in the magnetic circuit and to sustain thereby the oscillations of the oscillating bars.

2. An arrangement for electromechanically maintain ing the movement of a spiral balance wheel, comprising a bar of magnetic material diametrically rigid with the balance wheel and oscillating exclusively therewith, a magnetic circuit including a stationary section and a. stationary magnetic screen coaxially surrounding the path followed by the ends of said bar, extending at a short distance outside and throughout'the length of said path with the exception of two diametrically opposed narrow gaps magnetically cooperating with the stationary section andseparating the latter completely from the bar, the bar registering through its ends with the diametrically opposed gaps each time the balance wheel is in its medial position of unstable equilibrium, and an electric circuit wound over the stationary section of the magnetic circuit, entirely separated by the screen from the bar, and subje'cted to the short magnetic pulses produced by the movement of the bar in front of the gaps to produce thereby short modifications in the flux in the magnetic circuit to sustain the oscillations of the oscillating bar andbalance wheel.

3. An arrangement for electromechanically maintaining the movement of a spiral balance wheel, comprising a bar of permanent magnetic material diametrically rigid with the balance wheel and oscillating exclusively therewith, a magnetic circuit of magnetic material showing no substantial remanence, including a stationary section and a stationary magnetic screen coaxially surrounding the path followed by the ends of saidbar, extending at a short distance outside and throughout the length of said pathiwith the exception of two diametrically opposed narrow-gaps, magnetically cooperating with the stationary section and'separating the latter completely from the bar, the bar registering through its ends with the diametrically opposed gaps each time the balance wheel is in its medial positionof unstable equilibrium, and an electric circuit wound over the stationary section of the magnetic circuit, entirely separated by the screen from the bar, and subjected to the short magnetic pulses produce-d by the movement of the bar in front of the gaps to produce thereby short modifications in the flux in the magnetic circuit to sustain the oscillations of the oscillating bar and balance wheel.

4. An arrangement for electromechanically maintaining the movement of a spiral balance wheel, comprising a bar of permanent magnetic material diametrically rigid with the balance wheel and oscillating exclusively therewith, ama'gnetic circuit of magnetic material showing no substantial remanence, including a stationary section and a stationary magnetic screen coaxially surrounding the path followed by the ends of said bar, extending at a short distance outside'and throughout the length of said path withthe exception of two diametrically opposed narrow gaps, the angular, breadth of the ends of which are at the utmost equal .to about 20, magnetically cooperating with thestationary section and separating the latter completely from the bar, the bar registering through its ends with the diametrically opposed gaps each time the balance wheel is in its medial position of unstable equilibrium, and an electric circuit wound over the stationary section of the magnetic circuit, entirely separated by the screen from the bar, and subjected to the short magnetic pulses produced by the movement of the bar in front of the gaps to produce thereby short modifications in the flux in the magnetic circuit to sustain the oscillations of the oscillating bar and balance wheel.

5. An arrangement for electromechanically maintaining the movement of a spiral balance wheel, comprising over the stationary section of the magnetic circuit, entirely separated by the screen from the bar, and subjected to the short magnetic pulses produced by the movement 1 of the bar in front of the gaps to produce thereby short a bar of magnetic material diametrically rigid with the j balance wheel and oscillating exclusively therewith, a magnetic circuit including a stationary section and a stationary magnetic screen constituted by a cylindrical casing of a magnetic material showing no substantial remanence, coaxially surrounding the path followed by the ends of said bar, extending at a short distance outside and throughout the length of said path with the exception of two diametrically opposed narrow gaps, the breadth of which is substantially equal to that of the bar, magnetically cooperating with the stationary section and separating the latter completely from the bar, the bar registering through its ends with the diametrically opposed gaps each time the balance wheel is in its medial position of unstable equilibrium, and an electric circuit wound modifications in the flux in the magnetic circuit to sustain the oscillations of the oscillating bar and balance wheel.

6. An arrangement for electromechanically maintaining the movement of a spiral balance wheel, comprising a bar of permanent magnetic material diametrically rigid with the balance wheel and oscillating exclusively therewith, a magnetic circuit including a stationary section of a magnetic material showing no remanence, and a stationary magnetic screen coaxially surrounding the path followed by the ends of said bar, extending at a short distance outside and throughout the length of said path with the exception of two diametrically opposed narrow gaps, the angular breadth of each of which is substantially equal to that of the bar, magnetically cooperating with the stationary section and separating the latter completely from the bar, the bar registering through its ends with the diametrically opposed gaps each time the balance wheel is in its medial position of unstable equilibrium, the lines of force produced by the permanent magnets constituted by the bar closing solely through the screen when the balance wheel is away from its medial position and both through the screen and the stationary section when the balance wheel is approximately in said medial position, and an electric circuit wound over the stationary section of the magnetic circuit entirely separated by the screen from the bar, and subjected to the short magnetic pulses produced by the movement of the bar in front of the gap to produce thereby short modifications in the flux of the magnetic circuit to sustain the oscillations of the oscillating bar and balance wheel.

7. An arrangement for electro-mechanically maintainingthe movement of a spiral balance wheel, comprising a bar of magnetic material showing no remanence, diametrically rigid with the balance wheel and oscillating exclusively therewith, a magnetic circuit including a stationary section of permanently magnetized material and a stationary magnetic screen of magnetic material showing no substantial remanence, coaxially surrounding the path followed by the ends of said bar, extending at a short distance outside and throughout the length of said path with the exception of two diametrically opposed narrow gaps, magnetically cooperating with the stationary section and separating the latter completely from the bar, the bar registering through its ends with the diametrically opposed gaps each time the balance wheel is in its medial position of unstable equilibrium, the lines of force produced by the permanent magnet constituted by the stationary section closing solely through the screen when the balance wheel is away from its medial position and both through the screen and at least partly through the oscillating bar when the balance wheel is in a positlon approximating said medial position, and an electric circuit wound over the stationary section of the magnetic circuit, entirely separated by the screen from the bar, and subjected to the short magnetic pulses produced by the movement of the bar in front of the gaps to produce thereby short modifications in the flux in the magnetic circuit to sustain the oscillations of the oscillating bar and balance wheel.

8. An arrangement for electro-mechanically maintaining the movement of a spiral balance wheel, comprising a bar of magnetic material diametrically rigid with the balance wheel and oscillating exclusively therewith, a magnetic circuit including a stationary section and a stationary magnetic screen made of a magnetic material showing no substantial remanence, coaxially surrounding the path followed by the ends of said bar, extending at a short distance outside and throughout the length of said path with the exception of two diametrically opposed narrow gaps, the angular breadth of which is substantially equal to that of the bar, magnetically cooperating with the stationary section and separating the latter completely from the bar, the bar registering through its ends with the diametrically opposed gaps each time the balance wheel is in its medial position of unstable equilibrium, and an electric circuit wound over the stationary section of the magnetic circuit, entirely separated by the screen from the bar, and subjected to the short magnetic pulses produced by the movement of the bar in front of the gaps to produce thereby short modifications in the flux in the magnetic circuit to substain the oscillations of the oscillating bar and balance wheel, the magnetic material forming at least one of the following parts: the stationary section, the oscillating bar and the casing, being selected from sintered magnetic oxides having a resistivity above 0.1 ohm-cm. V

9. An arrangement for electromechanically maintaining the movement of a spiral balance wheel, comprising a bar of magnetic material diametrically rigid with the balance wheel and oscillating exclusively therewith, a magnetic circuit including a stationary section and a stationary magnetic screen coaxially surrounding the path followed by the ends of said bar, extending at a short distance outside and throughout the length of said path with the exception of two diametrically opposed narrow gaps, magnetically cooperating with the stationary section and separating the latter completely from the bar, the bar registering with the diametrically opposed gaps, through its ends, each time the balance wheel is in its medial position of unstable equilibrium, and an electric circuit wound over the stationary section of the magnetic circuit, entirely separated by the screen from the bar, and subjected to the short magnetic pulses produced by the movement of the bar in front of the gaps to produce thereby short modifications in the flux in the magnetic circuit to sustain the oscillations of the oscillating bar and balance wheel, and means locking the electric circuit against operation in the absence of said magnetic impulses.

10. An arrangement for electromechanically maintaining the movement of a spiral balance Wheel, comprising a bar of magnetic material diametrically rigid with the balance wheel and oscillating exclusively therewith, a magnetic circuit including a stationary section and a stationary magnetic screen coaxially surrounding the path followed by the ends of said bar, extending at a short distance outside and throughout the length of said path with the exception of two diametrically opposed narrow gaps, magnetically cooperating with the stationary section and separating the latter completely from the bar,

the bar registering with the diametrically opposed gaps, through its ends, each time the balance Wheel is in its medial position of unstable equilibrium, two windings surrounding different portions of the stationary section and the mutual coefficient of inductance of which is extremely small, means for feeding said windings with electric current, the modifications in the magnetic flux produced by the movement of the bar infront of the gaps acting on the current in the windings to produce in its turn modifications in the magnetic flux and thereby sustain the oscillations of the bar.

11. An arrangement for electromechanically maintaining the movement of a spiral balance wheel, comprising a bar of magnetic material diametrically rigid with the balance wheel and oscillating exclusively therewith, a magnetic circuit including a stationary section and a stationary magnetic screen coaxially surrounding the path followed by the ends of said bar, extending at a short distance outside and throughout the length of said path with the exception of two diametrically opposed narrow gaps, magnetically cooperating with the stationary section and separating the latter completely from the bar, the bar registering through its ends with the diametrically opposed gaps each time the balance wheel is in its medial position of unstable equilibrium, two windings separated from the bar by the screen, surrounding different portions of the stationary section and the mutual coefficient of inductance of which is extremely small, each winding being constituted by two interconnected half-windings the mutual coeflicient of inductance of which is substantially equal to zero, means for feeding said windings with electric current, the short magnetic pulses produced by the movement of the bar in front of the gaps acting on the current in the windings to produce in itst urn short modifications in the magnetic flux and thereby sustain the oscillations of the bar.

References Cited in the file of this patent UNITED'STATES PATENTS 2,704,334 Brailsford Mar. 15", 1955 2,719,944 Brailsford Oct. 4, 1955 2,769,946 Brailsford Nov. 6, 1956 FOREIGN PATENTS 198,725 Great Britain June 4, 1923 907,199 France .a June 18, 1945 910,563 Germany May3, 1954 1,092,411 France Nov. 10, 4 

